1. Field of the Invention
The present invention relates to a magnetic sensor comprising a magnetoresistive effect element and a coil for generating a magnetic field which is applied to the magnetoresistive effect element.
2. Description of the Related Art
Magnetic sensors have hitherto been known which employ as a magnetic field detection element a magnetoresistive effect element such as a giant magnetoresistive effect element (GMR element) or a magnetic tunnel effect element (TMR element). As shown in FIG. 33, such a magnetic sensor may comprise a coil 110 for applying a bias magnetic field to a magnetoresistive effect element 100. In this case, the coil 110 is formed spirally, and the magnetoresistive effect element 100 is formed above the spiral of the coil 110 ,and between the center of the spiral and the outermost circumferential part in a plan view. The bias magnetic field applied to the magnetoresistive effect element 100 is generated by electric current flowing through windings of the coil 110 positioned immediately below the magnetoresistive effect element 100.
However, according to the above prior art, the coil 110 includes large part that does not contribute directly to the forming of the bias magnetic field, which results in the large occupancy area of the coil 110 in the sensor, posing a problem that the coil 110 will be an obstacle to the miniaturization of the magnetic sensor. Another problem is that because the overall length of the coil 110 is increased with its increased resistance, the power consumption for generating the bias magnetic field will increase, or that because the electric current that might be necessary with a limited power supply voltage can not be secured, it will be difficult to form a desired bias magnetic field.
The present invention was conceived in order to address the above problems. According to a first aspect of the present invention there is provided a magnetic sensor comprising a thin-film-like magnetoresistive effect element; and a coil formed in a plane parallel to a planar film surface of the magnetoresistive effect element, the coil generating magnetic fields applied to the magnetoresistive effect element; wherein the coil comprises a first conductor forming a spiral in a plan view, and a second conductor forming a spiral in a plan view; wherein the magnetoresistive effect element is disposed between a spiral center of the first conductor and a spiral center of the second conductor in a plan view; and wherein the first conductor and the second conductor are connected such that electric currents in substantially the same direction pass through a part of the first conductor at a portion overlapping the magnetoresistive effect element in a plan view and through a part of the second conductor at a portion overlapping the magnetoresistive effect element in a plan view. The above magnetoresistive effect element can include a giant magnetoresistive effect element, a magnetic tunnel affect element, etc.
Thus, the magnetoresistive effect element is disposed between the spiral center of the first conductor that is spiral In a plan view and the spiral center of the second conductor that is spiral in a plan view, and an electric current in substantially the same direction passes through a portion of the first conductor at a portion to overlap the magnetoresistive effect element in a plan view and a portion of the second conductor at a portion to overlap the magnetoresistive effect element in a plan view. As a result, since large part of the conductor forming the coil can be used for generating the magnetic field applied to the magnetoresistive effect element, the occupancy area of the coil in the sensor can be reduced.
In this case, preferably, the part of the first conductor at the portion overlapping the magnetoresistive effect element in a plan view and the part of the second conductor at the portion overlapping the magnetoresistive effect element in a plan view are formed rectilinearly parallel to each other.
Thus, since an electric current flows in parallel with each of the conductors passing immediately under the magnetoresistive effect element (at a portion to overlap the magnetoresistive effect element in a plan view), each magnetic field generated by the electric current flowing in each conductor does not offset each other. Therefore, the magnetic field applied to the magnetoresistive effect element can be generated efficiently (without wasting the electric power).
Preferably, widths of the first and second conductors at the portion overlapping the magnetoresistive effect element in a plan view are equal, the widths being different from widths of the first and second conductors at the remaining portions.
Thus, the resistance value of the entire coil can be reduced, while an electric current of the magnitude necessary for generating a magnetic field of a predetermined magnitude is being applied to each conductor passing immediately under the magnetoresistive effect element, thereby making it possible to lower the power consumption.
In such a magnetic sensor, the coil can be used as a coil for generating a magnetic field to confirm whether or not the magnetoresistive effect element functions normally. In the case where the magnetoresistive effect element is a magnetoresistive effect element (e.g., a giant magnetoresistive effect element) including a free layer and a pin layer, the coil can be used as a coil to generate a magnetic field for initializing the direction of magnetization of the free layer. Further, in the case where the magnetoresistive effect element is a magnetic tunnel effect element, the coil can be used as a coil to generate a bias magnetic field for the magnetic tunnel effect element to detect the magnetic field applied to the element.
According to a second aspect of the present invention there is provided a magnetic sensor comprising a substrate; a first magnetic detection portion (unit) formed on the substrate, the first magnetic detection portion indicating a physical quantity which increases (which becomes larger) as the magnitude of a magnetic field in a first direction in a first orientation increases, the first magnetic detection portion indicating the physical quantity which decreases (which becomes smaller) as the magnitude of a magnetic field in the opposite direction to the first direction in the first orientation increases; a second magnetic detection portion formed on the substrate, the second magnetic detection portion indicating a physical quantity which increases (which becomes larger) as the magnitude of a magnetic field in a second direction in a second orientation that crosses (e.g., at right angles) the first orientation increases, the second magnetic detection portion indicating the physical quantity which decreases (which becomes smaller) as the magnitude of a magnetic field in the opposite direction to the second direction in the second orientation increases; a first testing coil disposed in the vicinity of the first magnetic detection portion (e.g., burled under the first magnetic detection portion within the substrate), for generating a magnetic field whose magnitude and direction change in the first orientation depending on electric current flowing therethrough, the first testing coil applying the generated magnetic field to the first magnetic detection portion; a second testing coil disposed in the vicinity of the second magnetic detection portion or buried under the second magnetic detection portion within the substrate, for generating a magnetic field whose magnitude and direction change in the second orientation depending on electric current flowing therethrough, the second testing coil applying the generated magnetic field to the second magnetic detection portion; an electric current supply source; a connection conductor for connecting the first testing coil and the second testing coil in series to the electric current supply source: and a conduction control circuit interposed in a closed circuit which comprises the electric current supply source, the first testing coil, the second testing coil and the connection conductor, for switching the states of the first testing coil and of the second testing coil into either a conductive state in which electric current from the electric current supply source flows therethrough or an unconductive state in which the electric current is shut off.
This magnetic sensor comprises at least two magnetic detection portions on the substrate. These magnetic detection portions may be the magnetoresistive effect element itself, or may be those that are formed by connecting a plurality of magnetoresistive effect elements, for example, in the form of a bridge circuit. The first magnetic detection portion, which is one of these magnetic detection portions, indicates a physical quantity which becomes larger as the magnitude of the magnetic field in the first direction in the first orientation increases, and indicates the physical quantity which becomes smaller as the magnitude of the magnetic field in the opposite direction to the first direction in the first orientation increases. The second magnetic detection portion, which is the other one, indicates a physical quantity which becomes larger as the magnitude of the magnetic field in the second direction in the second orientation that crosses the first orientation increases; and indicates the physical quantity which becomes smaller as the magnitude of the magnetic field in the opposite direction to the second direction in the second orientation increases. The physical quantity may be, for example, a resistance value, or may be a voltage value.
Furthermore, this magnetic sensor comprises the first testing coil for generating a magnetic field whose magnitude and direction change In the first orientation to apply the generated magnetic field to the first magnetic detection portion; the second testing coil for generating a magnetic field whose magnitude and direction change in the second orientation to apply the generated magnetic field to the second magnetic detection portion: the electric current supply source; the connection conductor; and the conduction control circuit. The first testing coil and the second testing coil are connected in series to the electric current supply source by the connection conductor. The state of the first testing coil and the second testing coil is controlled so that each of them can be in either a conductive state or an unconductive state. In this case, each of these testing coils (the first testing coil and the second testing coil) may be formed by connecting the first spiral conductor and second spiral conductor, or may assume a shape shown in FIG. 33.
With the above structure, since the first testing coil and the second testing coil are connected in series to the electric current supply source, the magnitude of electric current passing through one of these coils is always the same as the current passing through the other one of these coils. It is therefore possible to easily keep the ratio between the magnitude of the magnetic field applied to the first magnetic detection portion by the first testing coil and the magnitude of the magnetic field applied to the second magnetic detection portion by the second testing coil an expected value (e.g., xe2x80x9c1xe2x80x9d). As a result, it is possible to determine (it becomes worth determining) whether the ratio between the physical quantity indicated by the first detection portion and the physical quantity indicated by the second detection portion is the expected value (e.g., approximately xe2x80x9c1xe2x80x9d) or not.
In this respect, description will be made with using a concrete example. In this example, it is assumed that the first magnetic detection portion is configured so as to indicate the physical quantity of a first magnitude when the magnetic field of a predetermined magnitude in the first direction is applied, and that the second magnetic detection portion is configured so as to indicate the physical quantity of the same magnitude as the first magnitude when the magnetic field of the same magnitude as the predetermined magnitude in the second direction is applied. It is also assumed that the first testing coil is configured in a shape, the number of windings, and so on in a manner to apply a magnetic field of a predetermined magnitude Hb in the first direction to the first magnetic detection portion when an electric current of a predetermined magnitude (in a certain direction) is passing therethrough; and the second testing coil is configured in a shape, the number of windings, and so on in a manner to apply a magnetic field of the same magnitude as the predetermined magnitude Hb in the second direction to the second magnetic detection portion when an electric current of the same magnitude as the predetermined magnitude is passing therethrough in a predetermined direction.
In this case, according to the structure above, since the first testing coil and the second testing coil are connected in series to the electric current supply source, the electric current of the same magnitude is made flow through (or passes in) the first testing coil and the second testing coil, regardless of the characteristics of the conduction control circuit (e.g., regardless of resistance values of switching transistors in the case where the conduction control circuit comprises switching transistors for switching the state between the conductive state and the unconductive state). Therefore, the first testing coil and the second testing coil will apply the magnetic fields of the identical magnitude Hb in each corresponding direction to each corresponding magnetic detection portions.
Thus, the first and second magnetic detection portions are expected to indicate the physical quantity of the identical magnitude (i.e., the ratio is expected to be xe2x80x9c1xe2x80x9d). Therefore, if the difference of the physical quantities indicated by the first and second magnetic detection portions is larger than a predetermined value, it is possible to determine that the balance between the first and second magnetic detection portions is lost.
Specifically, unlike the features of the present invention, if the electric current supply source and the conduction control circuit for the first testing coil, and the electric current supply source and the conduction control circuit for the second testing coil are formed independently each other, it is difficult to apply the electric currents of the same magnitude to the first testing coil and the second testing coil because of the difference in the characteristics between the two electric current supply sources and because of the difference in the characteristics between the two conduction control circuits. As a consequence, in the configuration which does not use the present invention, the magnitude of the magnetic field generated by the first testing coil and the magnitude of the magnetic field generated by the second testing coil are sometimes not the same. Thus, even if the physical quantity indicated by the first magnetic detection portion and the physical quantity indicated by the second magnetic detection portion are different, the balance between both the detecting portions might not be lost. Therefore, it is not possible to determine that the balance between both the detecting portions is lost in such a situation.
Contrarily, according to the features of the present invention, since the first testing coil and the second testing coil are connected in series to share the electric current supply source and the conduction control circuit, the magnitude of electric currents passing through these coils are not different. It is therefore possible to certainly determine whether or not the balance in the characteristics between the first magnetic detection portion and the second magnetic detection portion is lost.
Note that the first testing coil and the second testing coil may be formed separately from the first magnetic detection portion and the second magnetic detection portion, or they may be formed within the same substrate (chip) with the first magnetic detection portion and the second magnetic detection portion. Particularly, if the first testing coil and the second testing coil are formed within the same substrate with the first magnetic detection portion and the second magnetic detection portion, a magnetic sensor which is a small and inexpensive single chip including testing portions (units) can be provided.
According to a third aspect of the present invention there is provided such a magnetic sensor, further comprising a detection circuit for selecting either the first magnetic detection portion or the second magnetic detection portion in response to an instruction signal from exterior, to detect a physical quantity indicated by the selected magnetic detection portion; and a control circuit for generating the instruction signal; wherein the first magnetic detection portion is configured so as to indicate the physical quantity of a first magnitude when the magnetic field of a predetermined magnitude is applied in the first direction in the first orientation, the first magnetic detection portion being configured so as to indicate the physical quantity of a second magnitude different from the first magnitude when the magnetic field of the predetermined magnitude is applied in the opposite direction to the first direction in the first orientation, wherein the second magnetic detection portion is configured so as to indicate the physical quantity of the first magnitude when the magnetic field of the predetermined magnitude is applied in the second direction in the second orientation, the second magnetic detection portion being configured so as to indicate the physical quantity of the second magnitude when the magnetic field of the predetermined magnitude is applied in the opposite direction to the second direction in the second orientation, and wherein when electric current of a predetermined magnitude flows in a predetermined direction through the first testing coil, the first testing coil applies a magnetic field of the predetermined magnitude in the first direction to the first magnetic detection portion and the second testing coil applies a magnetic field of the predetermined magnitude In the opposite direction to the second direction to the second magnetic detection portion, whereas when electric current of the predetermined magnitude flows in the opposite direction to the predetermined direction through the first testing coil, the first testing coil applies a magnetic field of the predetermined magnitude in the opposite direction to the first direction to the first magnetic detection portion and the second testing coil applies a magnetic field of the predetermined magnitude in the second direction to the second magnetic detection portion.
With above aspect, the magnetic field of the predetermined magnitude is applied to the first magnetic detection portion in the first direction in the first orientation when the electric current of the predetermined magnitude in the predetermined direction flows in the first testing coil. Therefore, if the detection circuit selects the first magnetic detection portion in accordance with the instruction signal from the external and detects the physical quantity indicated by the first magnetic detection portion, the detection results must be the physical quantity of the first magnitude (substantially the same magnitude as the first magnitude), as long as the selecting function of the detection circuit to select one of the magnetic detection portions is normal.
Similarly, the magnetic field of the predetermined magnitude is applied to the second magnetic detection portion In the opposite direction to the second direction, when the electric current of the predetermined magnitude in the predetermined direction flows in the first testing coil. Therefore, if the detection circuit selects the second magnetic detection portion in accordance with the instruction signal from the external and detects the physical quantity indicated by the second magnetic detection portion, the detection results must be the physical quantity of the second magnitude different from the first magnitude (substantially the same magnitude as the second magnitude), as long as the selecting function of the detection circuit to select one of the magnetic detection portions is normal.
Contrarily, in the case where the selecting function of the detection circuit is not normal, and the detection circuit selects the second magnetic detection portion although the instruction signal from the external indicates to select the first magnetic detection portion, the detection results of the detection circuit will be the physical quantity of the second magnitude (substantially the same magnitude as the second magnitude) which Is different from the first magnitude which is expected, when the electric current of the predetermined magnitude in the predetermined direction flows in the first testing coil, because the magnetic field of the predetermined magnitude is applied to the second magnetic detection portion by the second testing coil in the opposite direction to the second direction.
Similarly, in the case where the selecting function of the detection circuit is not normal, and the detection circuit selects the first magnetic detection portion although the Instruction signal from the external indicates to select the second magnetic detection portion, the detection results of the detection circuit will be the physical quantity of the first magnitude (substantially the same magnitude as the first magnitude) which is different from the second magnitude which is expected, when the electric current of the predetermined magnitude in the predetermined direction flows in the first testing coil, because the magnetic field of the predetermined magnitude is applied to the first magnetic detection portion by the first testing coil in the first direction.
That is, in the magnetic sensor configured as above, if the selecting function of the detection circuit is abnormal (i.e. the circuit is in a malfunction state), when the electric current of the predetermined magnitude in the predetermined direction is applied to the first testing coil, and when the physical quantity of the first magnetic detection portion is tried to be selected and detected in accordance with the instruction signal, the resulting (actual) detection amount will be the second magnitude while the first magnitude Is expected. Similarly, if the selecting function of the detection circuit is abnormal, when the electric current of the predetermined magnitude in the predetermined direction is applied to the first testing coil, and when the physical quantity of the second magnetic detection portion is tried to be selected and detected in accordance with the instruction signal, the resulting detection amount will be the first magnitude while the second magnitude is expected. Therefore, on the basis of such a combination of the instruction signal and the detection results, it is possible to determine whether or not the magnetic sensor (selecting function of the detection circuit) is abnormal.
It should be understood that, the same theory applies to the case where the control circuit makes the electric current of the predetermined magnitude In the opposite direction to the predetermined direction flow in the first testing coil. That is, if the selecting function of the detection circuit is abnormal and the electric current of the predetermined magnitude in the opposite direction to the predetermined direction is flowing in the first testing coil, when the physical quantity of the first magnetic detection portion Is tried to be detected In accordance with the instruction signal, the resulting detection amount will be the first magnitude while the second magnitude Is expected: or when the physical quantity of the second magnetic detection portion is tried to be detected in accordance with the instruction signal, the resulting detection amount will be the second magnitude while the first magnitude is expected. On the basis of such a combination of the instruction signal and the detection results, it is possible to determine whether or not the magnetic sensor (selecting function of the detection circuit) is abnormal.
Therefore, according to the magnetic sensor having such a structure, when there is a difference between the ideal detection value which is expected in accordance with the instruction signal from the external and the actual detection value, it is possible to determine that the detection circuit (magnetic sensor) is abnormal. It should be noted that, since various kinds of abnormality can be detected easily with such a structure as described above, it is optional whether to determine if the balance between the first magnetic detection portion and second magnetic detection portion is lost.